Production of calcium halophosphate phosphors

ABSTRACT

An improved process for the production of calcium halophosphate phosphors comprising forming a first substantially uniform admixture of (a) a calcium phosphate source selected from mono and di calcium orthophosphates, calcium pyrophosphates and mixtures thereof, (b) a secondary calcium source having a volatile anion, in stoichiometric proportions to form tricalcium orthophosphate, and (c) the desired sources of dopants, heating the first admixture under temperature and time conditions sufficient to form a doped tricalcium orthophosphate, forming a second uniform admixture, in proper molar ratios, of the doped tricalcium orthophosphates and the calcium halide forming ingredients and heating for a sufficient time and temperature to form a calcium halophosphate phosphor.

United States Patent Layman et al.

[54] PRODUCTION OF CALCIUM HALOPHOSPHATE PHOSPHORS [72] Inventors: Harry D. Layman, Ulster; Robert E.

Taylor, Towanda, both of Pa. 73] Assignee: Sylvania Electric Products Inc. [22] Filed: Sept. 8, 1970 21 App1 .No.: 70,550

[151 3,655,576 [451 Apr. 11, 1972 Primary Examiner-Robert D. Edmonds Attorney-Norman J. OMalley, Donald R. Castle and William H. McNeill [57] ABSTRACT An improved process for the production of calcium halophosphate phosphors comprising forming a first substantially uniform admixture of (a) a calcium phosphate source selected from mono and di calcium orthophosphates, calcium pyrophosphates and mixtures thereof, (b) a secondary calcium source having a volatile anion, in stoichiometric proportions to form tricalcium orthophosphate, and (c) the desired sources of dopants, heating the first admixture under temperature and time conditions sufficient to form a doped tricalcium orthophosphate, forming a second uniform admixture, in proper molar ratios, of the doped tricalcium orthophosphates and the calcium halide forming ingredients and heating for a sufiicient time and temperature to form a calcium halophosphate phosphor.

7 Claims, No Drawings BACKGROUND OF THE INVENTION 1. Field Of The Invention This invention relates to calcium halophosphate phosphors. More particularly, it relates to an improved process for producing calcium halophosphate phosphors.

2. Prior Art Calcium halophosphate phosphors are well known. These phosphors are useful as the luminescent coating inside the envelope of electric discharge lamps and devices. The calcium halophosphate phosphors all generally represented by the formula 3 Ca (PO,) :l Ca X wherein Ca X is a calcium halide such as fluoride or chloride'or can be a mixture of calcium fluoride and calcium chloride. The materials are doped with antimony and cadmium and sometimes manganese to obtain the desired color of emission.

These luminescent; materials have generally been prepared by heating and admixture of a calcium phosphate source such as monocalcium'hydrogen phosphate, a secondary calcium sourcesuch as calcium carbonate, the dopant sources, a halide source and a tertiary calcium source. Amounts of the various sources were chosen so to achieve the proper calcium to phosphorus and calcium to halide ratios and the desired amount of various dopants. The compounds used as. sources were such that the ions other than those specifically combined to form the calcium halophosphate evolved during heating to elevated temperatures. For example, ammonium halides were used as halide sources and calciumcarbonateswere used as secondary and tertiary calcium sources. The process produced satisfactory phosphors for many purposes, however, the phosphbrs were generally produced in trays and the dopant distribution was non-uniform, therefore, phosphors in various portions of the tray varied in dopant concentration. As can be appreciated, the uniformity of the luminosity of a lamp envelope coated with the phosphors varied in relationship to the uniformity of the phosphor. It is believed, therefore, a process that enables the production of a more uniformcalcium ,"halophosphate is an-advancementin the art.

OBJECTS AND SUMMARY OF THE INVENTION of monocalcium. hydrogen orthophosphate, dicalcium hydrogenorthophosphate, calcium pyrophosphate andmixtures thereof, an antimony source and a cadmium source, an amount-ofa secondary calcium source containing a volatile anion .to yield an overall (Ca Mn Cd Sb):P ratio of about 3:2, heating the admixture at a temperature and for a sufficient time to convert said admixture into an antimony-cadmium.dopedtricalcium orthophosphate, forminga second admixture: consisting essentially of the doped tricalcium orthophosphate, a tertiary calcium source and a halide source, the molar ratio of tricalcium ortho-phosphate to calcium to halide being from about 320.9:2 to about 3:l.2:2.5 respectively and heating said second admixture at a temperature and for a sufficientf timeto convert the admixture into a calcium halophosphate doped with antimony and cadmium.

F or a better understanding of the present invention, togeth'erwith other and further objects, advantages and capabilities thereof, reference is made to the following disclosure and appended claims in connection with of some of the aspects of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The calcium phosphate source that are suitable in the practice of this invention are monocalcium hydrogen orthophosphate CaHOP calcium dihydrogen orthophosphate, CA(HPO calcium pyrophosphate, CA P O and the like. Either anhydrous or hydrates of the foregoing calcium phosphates can be used along with a sufficient amount of a secondary calcium source to convert the phosphates present to tricalcium orthophosphate, Ca (PO,) The secondary calcium source can be any calcium compound that contains an anion that will evolve from the admixture during the subsequent heating step, or will decompose to form a volatile compound. Suitable sources include calcium carbonate, calcium hydroxide, calcium nitrate, calcium peroxide, and the like. Of these, calcium carbonate is preferred. A sufficient amount of the secondary calcium source is used to obtain a ratio of (Ca Mn Cd Sb):P of about 3:2 so that doped tricalcium orthophosphate, Ca (PO can be formed.

The source of the dopants, antimony and cadmium are also added to the blend. Generally, the source of the dopants will be the oxides, however, other sources such as cadmium carbonate, cadmium hydroxide, cadmium phosphate and antimony phosphate can be used. In most instances, from about 0.005 to about 0.05 moles of antimony and cadmium per mole of tricalcium orthophosphate will be used with from about 0.007 to about 0.015 moles of antimony per mole Ca (PO being especially preferred and from about 0.01 to about .015 moles of cadmium per mole Ca (PO being especially preferred.

After the first admixture consisting essentially of the foregoing components is prepared, it is heated in an inert atmosphere such as in nitrogen at a temperature of from about 1,200 C. to about 1,250 C. for a sufficient time to form a doped-crystalline tricalcium orthophosphate. Generally about I to about 6 hours are sufficient to form the crystalline material. Analysis of samples of the material can be used to determine the actual time required in the particular furnace system used.

After the doped crystalline tricalcium orthophosphate is formed, a second admixture is formed consisting essentially of the doped tricalcium orthophosphate, and a tertiary calcium source and a halide source in ratios to yield about 0.8 to about 1.2. mole of calcium halide per mole of tricalcium the above description orthophosphate. The preferred halides are a mixture of chloride and fluorides. The calcium source and halide source can be the appropriate calcium halide or be mixtures of individual calcium sources and halide source. For example, calcium fluoride, ammonium chloride and calcium carbonate in proper ratios can be used to produce a desirable calcium halophosphate or a calcium fluoride and calcium chloride blend can be used to provide the sources of calcium and halide. If a calcium fluoride-calcium chloride mixture is desired generally the ratio of F :C] is from about 3.5:1 to about 4.5: 1. If a tertiary calcium source other than the appropriate calcium halide is used it can be selected from the same group as the secondary calcium source and a Cazhalide ratio of 1:2 is used. Additionally, the secondary and tertiary calcium sources can be the same or different compounds. After the second substantially uniform admixture is prepared by blending using conventional solids blending equipment the admixture is heated to a temperature of from about 1140 C. to about 1180 C. for at least about 2 hours and preferably about 6 hours to form the calcium halophosphate.

To more fully illustrate the invention the following detailed examples are presented. All parts, proportions and percentages are by weight unless otherwise indicated.

EXAMPLE 1 A uniform blend of the following components are prepared:

The blend is heated in trays in an inert atmosphere of nitrogen in a furnace for about 3 hours at 1 150 C. to form a conventional calcium halophosphate, doped with manganese, anti-mony and cadmium. Three samples designated as l-A, 1-3 and I-C are taken from the trays at the top, middle and bottom respectively.

A uniform blend of the following components is prepared:

Weight Molar Equivalent CaHFO 3053.1 grams 2.0 CaCO, 888.5 grams 0.8 MnCO 86.6 grams 0.0633 Sb,O;, 80.9 grams 0.025 CdO 48.4 grams 0.034

The uniform blend is heated in an inert atmosphere of nitrogen in a furnace at a temperature of about 1,200 C. for about 4 hours. A crystalline tricalcium orthophosphate is formed.

A second uniform blend of the following components is prepared.

Weight Molar Equivalent Doped Q1 From blend 3780.0 grams 3.00 Cal- 279.8 grams 0.865 NH CI 100.5 grams 0.475 CaCO 96.7 grams 0.238

The foregoing blend is heated in trays in an inert atmosphere of nitrogen in a furnace at about 1 150 C. for about 4 hours to form a calcium halophosphate. Samples designated as ll-A, "-8 and ll-C are taken from the top, middle and bottom of the trays respectively.

Analysis of the samples indicate the following results in Table 1.

TABLE 1 LA [-8 l-C Cd 1.20 0.68 0.64 7% Sb 0.73 0.91 0.92

ll-A ll-B tt-c Cd 1.27 1.28 1.27 /2 Sb 1. 0.99 0.98

As can be seen from the above data the process of the present invention yields a product that is uniform throughout since essentially change in Cd or Sb content is evident.

EXAMPLE II ing data is obtained and given in Table 2.

TABLE 2 Brightness ln Lumens For 40 Watt Fluorescent Lamps Sample Sample In each instance, it is shown that the phosphors produced by the process of this invention have a higher brightness than the materials produced by the prior art methods.

While there has been shown and described what are at present considered the preferred embodiments of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the scope of the invention as defined by the appended claims.

What claimed is: claimed:

1. A process for producing a calcium halophosphate phosphor comprising:

a. forming a first substantially uniform admixture consisting essentially of a calcium phosphate source selected from the group consisting of monocalcium hydrogen orthophosphate, dicalcium hydrogen orthophosphate, calcium pyrophosphate and mixtures thereof, a sufficient amount of secondary calcium source containing a volatile anion, an antimony source and a cadmium course, to obtain a (Ca Cd Sb):PO ratio of about 3:2 in said admixture,

b. heating said first admixture in a substantially inert atmosphere to a temperature of from about l200 C. to about 1250 C. for at least about 60 minutes to form a doped tricalcium ortho-phosphate composition consisting essentially of tricalcium ortho-phosphate doped with antimony and cadmium, c. forming a second substantially uniform admixture consisting essentially of said doped tricalcium orthophosphate composition, a tertiary calcium source and a halide source wherein the ratio of tricalcium orthophosphate to calcium to halide is from about 3:0.9:2.0 to about 3:1.2:2.5, respectively, and

d. heating said second admixture to a temperature of from about 1140 C. to about 1180 C. for at least about 2 hours to form a calcium halophosphate phosphor.

2. A process according to claim 1 wherein said halide is a mixture of fluoride and chloride.

3. A process according to claim 2 wherein in said first admixture a manganese source is present.

4. A process according to claim 2 wherein in said second admixture a manganese source is present.

5. A process according to claim 2 wherein the ratio of tricalcium orthophosphate to calcium halide is from about 2.8:1 to about 3.0: l.

6. A process according to claim 5 wherein said calcium phosphate source is CaHOP 7. A process according to claim 6 wherein said secondary calcium source is calcium carbonate.

UNITEDSTATESPATE-NT"OFFICE (5/69) CERTIFICATE OF CORRECTION Patent 'No. a 655 a 576 i I v Dated April 97;

Inventor) Harry 1), Layman and Robert E. Tavlor 7 It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Col. 2', Line CaHOP should read "CaHPO Col. 4, Claim 6, line 2 "CaHOPa" should read- "CaHPO Signed and sealed this 29th day of-"August 1972.

(SEAL) Attest':

EDWARD M.FLETCHER,JR. Attesting Officer ROBERT GOTTSCHALK Commissioner of Patents 

2. A process according to claim 1 wherein said halide is a mixture of fluoride and chloride.
 3. A process according to claim 2 wherein in said first admixture a manganese source is present.
 4. A process according to claim 2 wherein in said second admixture a manganese source is present.
 5. A process according to claim 2 wherein the ratio of tricalcium orthophosphate to calcium halide is from about 2.8:1 to about 3.0:1.
 6. A process according to claim 5 wherein said calcium phosphate source is CaHOP4.
 7. A process according to claim 6 wherein said secondary calcium source is calcium carbonate. 